Data Acquisition Toolbox, single sample

Using Matlab's Data Acquisition Toolbox (and not using Simulink), how can i read and output single samples at a high rate, with the ability to adjust the data pseudo-realtime? I'm only looking for ~100 Hz. I'm familiar with streaming/acquiring large arrays of data at high rates, but i'd like to try controlling a system with a simple feedback loop -- so i'd like to only output and read one sample at a time.

Currently I get 1 Hz if just using the standard session.startForeground in a loop, with only one data point queued up for output. Why is it this slow?

I'm using a National Instruments USB-6215 DAQ.